The present invention relates to a still picture search/retrieval method for searching and retrieving a still picture from a database which stores a plurality of still pictures as data. The invention is also concerned with a still picture search/retrieval apparatus or system for carrying out the method.
In an extended database such as a so-called multi-media database which is capable of handling plural types or species of data such as characters, sound, still pictures and others, there may arise such a situation in which search or retrieval of only the sound and/or still pictures exclusive of the character string data is demanded. In such multi-media database, character strings indicative of features of the data to be stored are entered in an index table or field of the database as keywords which can serve as the keys upon performing the search. In the case of the still picture data, shapes or geometrical patterns, names, colors and the like are often used as the keywords.
By way of example, a still picture search/retrieval method based on the color is disclosed in JP-A-3-262079. According to this prior art method, when still picture data are to be stored in a database, a region of each still picture is designated and a representative color component of that region is determined. The representative color component data thus determined is additionally registered in an index field or table of the database upon storage of the still picture data. On the other hand, when a still picture of a color concerned is to be retrieved, a list of color samples extracted from all the still picture data stored in the database is displayed. By designating the color component of the color concerned by referencing the color sample list, the still picture having the color component as designated is retrieved to be displayed. In brief, this prior art still picture search method resides in that color components are extracted from the still pictures and the search of the still picture concerned is performed on the basis of the color components as extracted.
The conventional still picture search/retrieval methods such as mentioned above however suffer from numerous problems to be solved.
First, the still picture can not be searched with a color other than that of the region designated and registered previously. By way of concrete example, let's suppose a still picture depicting "a person putting on a red hat and wearing a white suit". When this still picture is registered in the database with the region covering "red hat", the still picture can not be retrieved with any other color than "red". In other words, it is impossible to search and retrieve the still picture with the color of the suit even when it is desired.
Further, since the keyword based on the color is registered as the index in the database, the amount of data stored in the database increases correspondingly, which is of course unfavorable from the standpoint of economy.
Besides, it is noted that the colors having color components differing from one another more or less are very difficult for the searcher to visually discern discriminatively. Consequently, when a still picture is to be searched and retrieved with only "pure red" having the R-, G- and B-primary color components of "256", "0" and "0", respectively) as the color of concern, it is practically impossible to discriminate the color "pure red" from a color "reddish" (i.e., nearly or approximately red). In this way, with the still picture search/retrieval method known heretofore according to which a region of a still picture is designated and the representative color component extracted from that region is registered upon storage of the still picture in a database, the still picture can be searched only with the color of the region designated and registered beforehand, to serious inconvenience.
Additionally, because the search is performed by checking actually the colors contained in the color samples for thereby selecting the color of concern, the still picture search/retrieval which tolerates more or less difference in the color is difficult to carry out.